Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $7.53   6.662%   $8.0316   $8.03   $8.05   $8.00  
  Purchase #2 $246.87   8.275%   $267.2985   $267.30   $267.30   $267.30  
  Purchase #3 $219.39   8.732%   $238.5471   $238.55   $238.55   $238.50  
  Purchase #4 $91.90   5.266%   $96.7395   $96.74   $96.75   $96.70  
  Purchase #5 $139.40   9.158%   $152.1663   $152.17   $152.15   $152.20  
  Purchase #6 $165.46   6.486%   $176.1917   $176.19   $176.20   $176.20  
  Purchase #7 $93.52   10.151%   $103.0132   $103.01   $103.00   $103.00  
  7 purchase totals = $964.07       $1,041.9879   $1,041.99   $1,042.00   $1,041.90